Home – Home – Jornals – Chemistry for Sustainable Development 2013 number 6

BIOMEC, a new two-stage process based on a short mechanochemical (MC) pre-treatment followed by biological treatment with purposely selected bacteria (Novosphingobium pentaromativorans), was investigated to detoxify Taranto’s harbour (S. Italy) marine sediments contaminated by polycyclic aromatic hydrocarbons (PAHs) and classified as hazardous waste, according the Italian law (Legislative Decree 152/2006). The experimental results, aimed at determining the overall efficiency of the BIOMEC treatment, indicated that PAHs degradation may be achieved in a very effective (97 %) and fast (<14 days) manner, yielding a non-toxic waste largely reusable as building material. In particular the MC pre-treatment allowed bigger degradation of high MW PAHs; because of their larger aromatic structure, after collisions between sediment particles and milling bodies these congeners may generate more stable free radicals with respect to low MW ones and the probability of their formation is higher, hence they are MC degraded to larger extent. GC-MS analysis of MC degradation products of benzo(a)pyrene (BaP), spiked on clean sediment (taken from Taranto’s harbour too), suggest that the first probable step is an almost complete destruction of BaP rings and the formation of oxidized heavy molecules with residual aromaticity. Then the breakdown of this kind of compounds and the formation of small radicals give origin to many volatile organic molecules which, through an accretion process, form heavier compounds up to graphitization.

It has recently been shown that Severe Plastic Deformation (SPD), and particularly cold rolling, techniques could be used to obtain nanostructured metal hydrides with enhanced hydrogen sorption properties. Cold rolling is a particularly interesting technique because it is easily scalable to industrial level. We present here the effect of cold rolling on hydrogen storage properties of magnesium and magnesium hydride (MgH₂). Commercial magnesium and magnesium hydride were processed in a vertical cold rolling apparatus. For pure magnesium, a highly textured material was obtained after only one roll and first hydrogenation was faster than unprocessed magnesium. In the case of magnesium hydride, after only five rolling passes hydrogen sorption kinetics at 623 K were greatly enhanced without noticeable loss of capacity. The improvement in sorption kinetics is attributed due to the nanocrystalline structure and number of created defects. Investigation of the powder morphology and crystal structure indicates that cold rolling is equivalent to ball milling.